Cowell has praised the "loyalty" of the other members of One Direction, Louis Tomlinson, Harry Styles and Niall Horan, but failed to mention their bandmate, who recently signed a solo deal with Capitol Records, reported Female First.
"We're in touch with them all. The great thing about all these boys, well not all of them but most of them, they are incredibly loyal and you don't always expect that.
"Niall, Harry, Louis - amazing."
Tomlinson recently joined Simon on "America's Got Talent" as a guest judge and the 56-year-old star was very impressed with how the "History" singer, who shot to fame after being put into 1D on "The X Factor" in 2010, fared with the contestants.